Posted
by
Soulskillon Tuesday January 19, 2010 @10:33AM
from the any-old-port-in-the-storm dept.

An anonymous reader writes "With HDMI becoming increasingly common, Displayport has been slow to emerge as a widely used connection interface, but a plethora of new features in the new v1.2 standard could see that change. As well as doubling the data rate of the existing v1.1a standard to 21.6 Gbps, the update allows for multiple monitors to be connected to a single Displayport connector and adds support for transporting USB data at up to 720Mbps, enabling embedded webcams, speakers and USB hubs over a single cable. Ethernet data is also supported. The improved data rate will allow for richer, larger and higher resolution displays, and the new version is also backward compatible with the current display technology, so all the ports, cables and devices will be interchangeable, although they will revert to the lowest common denominator."

I hate Apple as much as the next guy, but not mentioning them at all in the summary is a bit... crude. Also, here's a list of all the new stuff (taken from http://www.hardmac.com/news/2010/01/11/displayport-1-2-validated [hardmac.com]).
* Doubling bandwidth mostly to support 3D: 21.6 Gbits/s.
* Connect even more monitors from a single DisplayPort. Dedicated hubs should soon be available.
* As for the HDMI, transport USB data between a computer and a display, supporting Display USB functions such as a webcam and USB hub.
* Connect to display with 3840 x 2400 resolution at 60Hz, or a 3D display (120Hz) at 2560 x 1600.
* Audio Copy Protection and category codes
* High definition audio formats (such as Dolby MAT, DTS HD, all BD formats,etc.)
* Synchronization assist between audio and video, multiple audio channels, and multiple audio sink devices using Global Time Code (GTC)

HDMI needs additional chips/control circuits on the transmitting and receiving end to deal with encoding and decoding. Display Port is directly compatible with the display panels themselves and as such

...can't display motion pictures published by six American companies. Home users who expect to watch high-definition feature films will choose an interconnect that does "encoding and decoding" because the publishers of feature films on high-definition home video demand "encoding and decoding" for digital restrictions management. Sure, DisplayPort 1.1 and later allow for DPCP, but then you lose the advantage of no "encoding and decoding".

Multiple display support, for one. You can use DisplayPort to daisy chain multiple screens. While there is a dual-link spec for HDMI, it only supports 2 display devices and isn't supported by anyone.

Also, DisplayPort was designed from the ground up for bidirectional communication (ie- touch input, camera, mic input, etc). These features have only recently been shoehorned into the HDMI 1.4 spec, and may be some time before one can actually use it.

Depends. Some devices can produce DisplayPort and HDMI (DVI-D) signals. You can get a cheap adaptor for these that just changes the physical form factor of the connector. The formats for HDMI and DisplayPort are very different though, so if this isn't supported by your hardware then you need something that will decodes one signal and produces the other signal after buffering a frame. This is how the DisplayPort to Dual Link DVI adaptors that Apple sells work, and if you check the reviews you'll see that they are very unreliable.

Please, buy one of those and plug it into a DisplayPort and expect it to magically transform it into DVI.

It's designed to plug into the Mini DisplayPort on new MacBooks. These contain both DisplayPort and DVI electronics. When you plug in an monitor using the adaptor, the graphics hardware detects the presence of an HDMI device and switches to HDMI mode. The reason that the adaptor is cheap is that the laptop is doing all of the work, being able to produce both DVI and DisplayPort signals.

DisplayPort 1.1+ includes HDCP just like HDMI does. It is enabled on all Apple products, and Blu-ray manufacturers are required to enable it as well. Thus any display manufacturer that wants to work with those segment of the markets will also include HDCP support.

Even though the price of optical equipment is drastically dropping, it's still quite a bit more expensive than your regular ol' Al/Cu-wire-to-chip solution. Until data volumes become so immense that the noise level for even those connections is unacceptable, so too will the price of optical connections.

Just look at the optical audio equipment; unless you're a middle-to-high end user, you probably still use the ol' copper wires to hook up your receiver rather than the fancy $20 optical digital audio cable.

With digital video you can use a nice long extension cable with no loss of quality.

Have you ever actually tried this? DVI and HDMI are balanced connections, and they were never designed for long runs-more than 6 feet will sometimes get "sparkle" from digital artifacts. VGA works much better for long runs, although it's preferable to break it out into 5 full sized coax cables. This is not an option with HDMI, and that's a big reason why a lot of installers hate messing with it.

DisplayPort itself uses a completely different kind of signalling than HDMI. An HDMI signal is basically just a digital version of the video stream... it runs three differential TMDS data links and one clock link at 10x the rate of the display's pixel clock, very tightly coupled to the video. Native DisplayPort sends packetized data, and the signal is over 1, 2, or 4 differential serial lines, with clocking information embedded in that signal.

HDMI 1.3 supports 10.2Gb/s per link (there's a dual link version, but it's not common), and resolutions up to 2560×1600p75 for 24-bits per pixel or 1920x1200p60 for 48-bits per pixel. HDMI 1.4 adds a 100Mb/s ethernet channel and support for displays up to 4096x2160p24 at 24 bits per pixel (same bandwidth, more formats).

DisplayPort 1.1 supports a throughput of 8.64 Gb/s across the four links, which goes to 17.2 Gb/s in version 1.2 (the 21.6Gb/s is the symbol rate over 8b/10b encoded links).

In short, they're completely different. However, the spec does allow a DisplayPort connector to switch and spit out HDMI/DVI compatible signals instead. There is no requirement that DisplayPort connectors do this, however.

So any in-cable passive DisplayPort to HDMI cable is counting on this HDMI bridge feature being in the device you're using. An "active" cable will convert the video signal (well, a simple one), but lose the 2-way data features.

Expenses. The Sony/Philips optical is about the only consumer optical in common use, but that's over plastic, driven by LEDs. Pretty cheap. For optical at these rates, you'd need real lasers (LEDs peak around 500Mb/s) something like 10GBASE-R or 10GBASE-SR cable (LOMMF/OM3). None of that's crazy expensive... unless you compare it to electrical. And in particular, the electrical that the equipment makers are actually paying for.

Keep in mind, these are the industry guys who got together to create DisplayPort, at least in part because they got bent out of shape having to pay US$0.04 per device to use HDMI. They're not likely to replace a $0.50 electrical connector with a $2.00 optical connector and $5.00+ laser. And of course, lasers go one way... you actually need a laser at each end, if you want 2-way traffic. Or a custom cable, with electrical backchannel.

Well, why not.. I have some video cables around here with integrated optical audio channel.

So this is the next one up, after DisplayPort, but designed as a general purpose standard: Light Peak. I think this started out as an optical answer to Firewire at Apple, but rather than do it themselves, change too much for the spec, and have Intel (and the rest of the PC industry) go and create an alternative, this time Apple brought it to Intel. Maybe.. at least that's one story.

The nice thing about Light Peak... it's fast enough to do the HDMI/DisplayPort thing. And replace SATA, USB, Firewire, anything else you want. Of course, like all optical interconnects, the connectors are an issue (dirt kills), and unless they go to some kind of FDM, they'll need one cable in each direction, just like 10Ge uses in its various optical forms. Then there's the issue of power... we're kind of used to USB and Firewire cables providing power for small devices. But it's still a work in progress, 10Gb/s on launch, up to 100Gb/s on the roadmap.